Thermal behaviour, compatibility study and decomposition kinetics of glimepiride under isothermal and non-isothermal conditions

In the present work, the thermal decomposition of glimepiride (sulfonylurea hypoglycemic agent) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry (TG/DTG). Isothermal and non-isothermal methods were employed to determine kinetic data of decomposition process. The physical chemical properties and compatibilities of several commonly used pharmaceutical excipients (glycolate starch, microcrystalline cellulose, stearate, lactose and Plasdone®) with glimepiride were evaluated using thermoanalytical methods. The 1:1 physical mixtures of these excipients with glimepiride showed physical interaction of the drug with Mg stearate, lactose and Plasdone®. On the other hand, IR results did not evidence any chemical modifications. From isothermal experiments, activation energy (E _a) can be obtained from slope of lnt vs. 1/T at a constant conversion level. The average value of this energy was 123 kJ mol^–1. For non-isothermal method E _a can be obtained from plot of logarithms of heating rates, as a function of inverse of temperature, resulting a value of 157 and 150 kJ mol^–1, respectively, in air and N₂ atmosphere, from the first stage of thermal decomposition.     

Thermal behavior study and decomposition kinetics of salbutamol under isothermal and non-isothermal conditions

The thermal decomposition of salbutamol (β₂ — selective adrenoreceptor) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry (TG/DTG). It was observed that the commercial sample showed a different thermal profile than the standard sample caused by the presence of excipients. These compounds increase the thermal stability of the drug. Moreover, higher activation energy was calculated for the pharmaceutical sample, which was estimated by isothermal and non-isothermal methods for the first stage of the thermal decomposition process. For isothermal experiments the average values were E _act=130 kJ mol⁻¹ (for standard sample) and E _act=252 kJ mol⁻¹ (for pharmaceutical sample) in a dynamic nitrogen atmosphere (50 mL min⁻¹). For non-isothermal method, activation energy was obtained from the plot of log heating rates vs. 1/T in dynamic air atmosphere (50 mL min⁻¹). The calculated values were E _act=134 kJ mol⁻¹ (for standard sample) and E _act=139 kJ mol⁻¹ (for pharmaceutical sample).     

Thermal decomposition and non-isothermal decomposition kinetics of carbamazepine

The thermal stability and kinetics of isothermal decomposition of carbamazepine were studied under isothermal conditions by thermogravimetry (TGA) and differential scanning calorimetry (DSC) at three heating rates. Particularly, transformation of crystal forms occurs at 153.75°C. The activation energy of this thermal decomposition process was calculated from the analysis of TG curves by Flynn-Wall-Ozawa, Doyle, distributed activation energy model, ?atava-?esták and Kissinger methods. There were two different stages of thermal decomposition process. For the first stage, E and logA [s^?1] were determined to be 42.51 kJ mol^?1 and 3.45, respectively. In the second stage, E and logA [s^?1] were 47.75 kJ mol^?1 and 3.80. The mechanism of thermal decomposition was Avrami-Erofeev (the reaction order, n = 1/3), with integral form G(α) = [?ln(1 ? α)]^1/3 (α = ～0.1–0.8) in the first stage and Avrami-Erofeev (the reaction order, n = 1) with integral form G(α) = ?ln(1 ? α) (α = ～0.9–0.99) in the second stage. Moreover, ΔH ^≠, ΔS ^≠, ΔG ^≠ values were 37.84 kJ mol^?1, ?192.41 J mol^?1 K^?1, 146.32 kJ mol^?1 and 42.68 kJ mol^?1, ?186.41 J mol^?1 K^?1, 156.26 kJ mol^?1 for the first and second stage, respectively.     

3,4-二硝基吡唑热分解及非等温动力学

采用TG-DSC综合热分析的方法,对3,4-二硝基吡唑(DNP)的热分解和非等温动力学进行了研究。结果表明DNP的热分解分两阶段进行,并且在升温速率达到15K/min时才能明显区分。分别采用Archar微分法和Coats-Redfen积分法计算了DNP第一阶段热分解反应动力学参数:Ea=91.6kJ.mol-1,lnA=42.7s-1。最可能的DNP热分解机理为随机成核和随后生长机理,符合动力学机理函数Avrami-Erofeev方程,n=3。     

Comparative kinetic study of decomposition of some diazepine derivatives under isothermal and non-isothermal conditions

Thermal analysis is one of the most widely used methods for studying the solid state of pharmaceutical substances. TG/DTG and DSC curves provide important information regarding the physical properties of the pharmaceutical compounds (stability, compatibility, polymorphism, kinetic analysis, phase transitions etc.). The purpose of a kinetic investigation is to calculate the kinetic parameters and the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances. A kinetic study regarding the diazepam, nitrazepam and oxazepam thermal decomposition was performed, under non-isothermal and isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 483, 498, 523, 538 and 553 K. The TG/DTG data were processed by three methods: isothermal model-fitting, Friedman’s isothermal-isoconversional and Nomen-Sempere non-parametric kinetics. In the model-fitting methods the kinetic triplets (f(α), A and E _a) that defines a single reaction step resulted in being at variance with the multi-step nature of diazepines decomposition. The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation energies on the extent of conversion. It is very difficult to obtain an accord with the similar data which resulted under non-isothermal conditions from a previous work. The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as well as a different strategy of experimental data processing.     

Crystallization kinetics of isotactic polypropylene nucleated with octamethylenedicarboxylic dibenzoylhydrazide under isothermal and non-isothermal conditions

Octamethylenedicarboxylic dibenzoylhydrazide (TMC-300) was used as a nucleating agent for isotactic polypropylene (iPP) for the first time. The Avrami method and the Caze method were used to analyze the isothermal and non-isothermal crystallization kinetics of iPP incorporated with TMC-300, respectively. During isothermal crystallization, the half crystallization time at 130 °C reduces from 130 s of virgin iPP to 44 s after addition of TMC-300, which reflects that TMC-300 increased the crystallization rate of iPP obviously. The crystallization activation energy decreases from 382.5 kJ mol^?1 of virgin iPP to 275.3 kJ mol^?1 of iPP/TMC-300. During non-isothermal crystallization, the crystallization peak temperature of iPP nucleated with TMC-300 was increased by 5.1 °C when compared to that of virgin iPP at the cooling rate of 20 °C min^?1, and both the reduction of half crystallization time and the increase in peak crystallization temperature also justified that the addition of TMC-300 accelerated the crystallization of iPP.

     

Model-free method for isothermal and non-isothermal decomposition kinetics analysis of PET sample

Pyrolysis, one possible alternative to recover valuable products from waste plastics, has recently been the subject of renewed interest. In the present study, the isoconversion methods, i.e., Vyazovkin model-free approach is applied to study non-isothermal decomposition kinetics of waste PET samples using various temperature integral approximations such as Coats and Redfern, Gorbachev, and Agrawal and Sivasubramanian approximation and direct integration (recursive adaptive Simpson quadrature scheme) to analyze the decomposition kinetics.The results show that activation energy (E_α) is a weak but increasing function of conversion (α) in case of non-isothermal decomposition and strong and decreasing function of conversion in case of isothermal decomposition. This indicates possible existence of nucleation, nuclei growth and gas diffusion mechanism during non-isothermal pyrolysis and nucleation and gas diffusion mechanism during isothermal pyrolysis. Optimum E_α dependencies on α obtained for non-isothermal data showed similar nature for all the types of temperature integral approximations.     

Kinetic of sorbitol decomposition under non-isothermal conditions

The thermal behavior of sorbitol was studied under non-isothermal conditions, in both air and nitrogen atmosphere. The main process is a deep and continuous dehydration. For the kinetic analysis, the TG/DTG data obtained at five heating rates were processed by three different methods: Friedman, Budrugeac-Segal and non-parametric kinetic, respectively. This analysis indicates a complex reaction with a preponderant chemical process, described by a conversion function (1−α)^3/2, accompanied by diffusion.     

Kinetic of decomposition of some complexes under non-isothermal conditions

Kinetics of thermal decomposition of three structurally similar complexes Co₂Cu(C₂O₄)₃ (R-diam)₂, where R is ethyl, 1,2-propyl or 1,3-propyl, was studied under non-isothermal conditions and nitrogen dynamic atmosphere at heating rates of 5, 7, 10, 12 and 15 K min⁻¹. For data processing the Flynn-Wall-Ozawa and a modified non-parametric kinetic methods were used. By both methods the activation energy are in the range of 97–102 kJ mol⁻¹. The formal kinetic is r=kα(1−α)². Also a compensation effect between lnA and E was evidenced. The kinetic analysis lead to the conclusion of an identic decomposition mechanism by a single step process.     

Thermal decomposition of polymeric materials: Characteristics of kinetics at non-isothermal heating

General conclusions are made based on the results of experimental and theoretical investigations of the decomposition kinetics of various polymeric materials in a wide range of heating rates. It was found that the decomposition process of the investigated materials proceeds within confined temperature intervals. Kinetic equations are suggested to describe the thermal decomposition processes of polymers and natural coals, based on the characteristic revealed.     

Thermal study on decomposition of LiBH4 at non-isothermal and non-equilibrium conditions

Thermal decomposition measurements for lithium borohydride (LiBH₄) are performed at non-isothermal and non-equilibrium conditions by means of differential thermal analysis (DTA). A simplified alternative procedure is introduced for evaluating thermodynamic and kinetic parameters simultaneously using a single set of measurements. Rate constant (k) and enthalpy (ΔH = ?102.1 ± 0.7 kJ mol^?1 LiBH₄) are archived. Temperature dependence for activation energy (E _a) is found taking advantage of Guggenheim–Arrhenius method; the mean activation energy is $ \overline{E}_{a} $  93.9 ± 0.9 kJ mol^?1 LiBH₄ in the range of heating rate β 1–50 K min^?1.     

Thermal hazardous evaluation of autocatalytic reaction of cumene hydroperoxide alone and mixed with products under isothermal and non-isothermal conditions

Journal of Thermal Analysis and Calorimetry - Severe fire and explosions are frequent phenomena during handling of organic peroxides that are promoted supremely by conditions such as chemical...     

The correlation between isothermal and non-isothermal kinetics in thermogravimetry

It is shown that the total differential of the function of the amount of conversion versus temperature and time (=f(T, t)) is equal to zero non-isothermal kinetics at constant heating rate. Hence, the mathematical expression used in the literature for the rate of the non-isothermal transformation, , is not valid.     

Thermal behaviour and non-isothermal decomposition kinetics of some Nd(III) coordination compounds

The authors present the results concerning the thermal behaviour of three polynuclear coordination compounds of Nd(III) and Co(II) or Fe(III) with triptophan. For the dehydration steps the values of the non-isothermal kinetic parameters have been determined.     

Thermal stability and non-isothermal decomposition kinetics of a polynuclear coordination compound precursor of copper ferrite

Results are presented on the thermal behaviour of [Fe(III)₂Cu(C₂C₄)₂(OH)₄(H₂O)₂] precursor of copper ferrite. An investigation of the decomposition steps and intermediates was followed by a non-isothermal kinetic analysis of the processable steps.